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Abstract

The average lifetime cost of care for people with Multiple Sclerosis (PwMS) in the United States is approximately $2.2 million per person affected, and up to 80% of PwMS are unemployed within 10 years of disease onset. MS-related fatigue is a debilitating symptom experienced by around 90% of PwMS, it can significantly affect an individual’s functional quality of life by interfering with activities of daily living (ADLs), causing reduced work performance, and contributing to loss of employment. MS-related fatigue is an umbrella term that encompasses the individual’s perceptions of fatigue (perceived fatigue) and measurable deterioration in performance (fatigability). Perceived fatigue and fatigability interfere with the individual’s efficient performance of physical and cognitive tasks and both should be considered during the assessment and management of MS-related fatigue. What further makes MS-related fatigue complex is that not only the disease process itself can cause fatigue, but also other prevalent comorbidities likely contribute to fatigue in MS such as depression and sleep disturbances. Therefore, the approach undertaken in the current body of research was under the notion that a multidisciplinary approach would seem best to optimally assess fatigue in PwMS. Perceived fatigue in PwMS is measured using self-reported scales which are used extensively in the MS-related fatigue field of research. However, there have been recent concerns regarding the psychometric properties of commonly used perceived fatigue scales in PwMS. This is an issue as interpreting the findings of those previous studies is now somewhat difficult. The current study utilized a more psychometrically sound perceived fatigue scale that has been validated for use in PwMS, called the Neurological Fatigue Index (NFI-MS). What makes the NFI-MS a unique measure of perceived fatigue in PwMS is that to our knowledge, it is the only perceived fatigue scale that includes two sleep components acknowledging the importance of considering sleep quality during the assessment of fatigue. Chapter 2 attempted to explore the relationship between the NFI-MS and measures of physical and cognitive fatigability. Previous evidence showed conflicting results regarding the relationship between perceived fatigue and fatigability, as some showed associations while others did not. Fatigability is distinguished from perceived fatigue by the concept of change, i.e., a measurable difference in the performance of a task over a period of time. We initially hypothesized that there are certain items on the NFI-MS that objectify the performance ability of the individual and therefore can be associated with fatigability. A total of 52 ambulatory participants took part in this cross-sectional design study. Physical fatigability was measured using percent change in meters walked on the Six Minute Walk Test and percent change in force exerted on a repetitive maximal hand grip test. Cognitive fatigability was measured by Response Speed Variability on the Continuous Performance Test. The fatigability measures utilized in this study have been previously utilized before and where further modified in both administration and scoring in the current study to better capture fatigability in our study sample. Perceived physical and cognitive fatigue were measured using the NFI-MS. Current perceptions of fatigue were examined immediately before and after performing the fatigability measures using a 1-item Visual Analogue Fatigue Scale. The results of Chapter 2 showed that cognitive fatigability was significantly associated with the NFI-MS physical domain and NFI-MS cognitive domain. However, physical fatigability was not associated with the NFI-MS. All participants demonstrated significantly higher perceptions of current fatigue after performing the physical and cognitive fatigability measures. The findings suggest that the NFI-MS appears to capture the cognitive aspect of MS-related fatigue (meaning it captures both perceived cognitive fatigue and cognitive fatigability), but not the physical aspect (only captures perceived physical fatigue not physical fatigability), and the fatigability measures utilized were fatiguing to the participants which is a clinically important finding. We can conclude that both perceptions of fatigue and fatigability should be measured collectively for a comprehensive assessment of fatigue in PwMS. Next, because an extensive body of evidence demonstrated a strong relationship between perceived fatigue and self-reported sleep quality, but conflicting results regarding the association between perceived fatigue and objective sleep quality; we aimed in Chapter 3 to explore the relationship between the NFI-MS and self-reported and objective sleep quality measures which have never been explored before. All participants filled out the Pittsburgh Sleep Quality Index to asses sleep quality, and the Epworth Sleepiness Scale to assess daytime sleepiness. To objectively quantify sleep quality, the participants wore an actigraph device on their dominant wrist for one week after the assessment day. The results indicated that higher perceived fatigue is significantly associated with poorer self-reported sleep quality and excessive daytime sleepiness, but not with objective sleep quality. Our findings from Chapter 3 support previous research that showed higher perceived fatigue measured using other scales is associated with poorer self-reported sleep quality and daytime sleepiness. Regarding the lack of association between perceived fatigue and objective sleep quality, we argued that perhaps there is a limitation of actigraphy to accurately assess sleep in this sample, as evidence showed that the actigraph may overestimate sleep efficiency and total sleep time. Furthermore, actigraphy findings might be limited by wear time. Perhaps PwMS need to wear the actigraph for more than one week to accurately assess their sleep quality. A previous study that found significant associations between actigraphy and fatigue had the participants wear the actigraph for two weeks. Based on our findings we encourage a wider use of the NFI-MS in clinical and research settings to assess and manage the role sleep quality has on perceived fatigue in the MS population. The relationship between sleep quality and fatigability has never been explored before. Due to the involvement of central nervous system dysfunction mechanisms of both MS-related fatigue and sleep disturbances, and due to the evidence that shows a relationship between perceived fatigue and poor sleep quality, we hypothesized that there would be an association between higher physical and cognitive fatigability and poor sleep quality in our study sample. The results of Chapter 4 showed that several components of the Pittsburgh Sleep Quality Index and several actigraph parameters were significantly associated with physical fatigability and cognitive fatigability. We provide the first body of evidence showing the relationship between poor sleep quality and fatigability in PwMS. Fatigability is an important construct of MS-related fatigue that is a common debilitating symptom in the MS population, and more emphasis should be put on considering the role of sleep quality on exacerbating MS-related fatigue. In summary, the work presented in this dissertation expands on the body of evidence showing the relationship between perceived fatigue, fatigability, and sleep quality in PwMS. Our experiments and findings are novel and significant through the use of the NFI-MS as a measure of perceived fatigue and through the assessment of the association between sleep quality and fatigability in PwMS. For a comprehensive and multidimensional assessment of MS-related fatigue, the measures used in this study can be easily administered in clinical and research settings. In addition, more emphasis should be put on considering the role of sleep quality on exacerbating MS-related fatigue in those with the mild-disease forms of MS. Around 70% of PwMS report some sort of a sleep disturbance, and up to 50% have a diagnosable sleep disorder. Poor sleep quality in PwMS has been associated with a reduction in several quality of life indices, including physical function, psychological well-being, self-care, work ability, and interpersonal relationships. Clinicians and therapists may need to consider sleep assessment and treatment as part of the MS-related fatigue management plan.